using AcDream.App.Rendering.Packs;
using AcDream.Plugin.Abstractions.Rendering;

namespace AcDream.App.Tests.Rendering.Packs;

/// <summary>
/// Campaign VM VM6: <see cref="RenderPackAtmospherePolicyEvaluation.FoliageWind"/>
/// (the exact per-day-group mean/gust lookup) and
/// <see cref="RenderPackAtmospherePolicyEvaluation.EaseTowardTarget"/> (the
/// smoothing step that keeps a day-group change from snapping).
/// </summary>
public sealed class RenderPackAtmospherePolicyEvaluationTests
{
    [Fact]
    public void FoliageWindLooksUpExactDayGroupMatchOnly()
    {
        FoliageWindDayGroupPoint[] table =
        [
            new(0, 0.25, 0.15),
            new(1, 0.45, 0.30),
            new(2, 0.60, 0.35),
            new(3, 0.85, 0.60),
        ];

        (float mean, float gust) = RenderPackAtmospherePolicyEvaluation.FoliageWind(table, 3);

        Assert.Equal(0.85f, mean);
        Assert.Equal(0.60f, gust);
    }

    [Fact]
    public void FoliageWindReturnsZeroForADayGroupAbsentFromTheTable()
    {
        FoliageWindDayGroupPoint[] table = [new(0, 0.25, 0.15)];

        (float mean, float gust) = RenderPackAtmospherePolicyEvaluation.FoliageWind(table, 99);

        Assert.Equal(0f, mean);
        Assert.Equal(0f, gust);
    }

    [Fact]
    public void FoliageWindReturnsZeroForANullTable()
    {
        (float mean, float gust) = RenderPackAtmospherePolicyEvaluation.FoliageWind(null, 0);

        Assert.Equal(0f, mean);
        Assert.Equal(0f, gust);
    }

    [Fact]
    public void FoliageWindDoesNotInterpolateBetweenDayGroupIndices()
    {
        // Day-group ids are not ordered by "how windy" — index 1 sitting
        // between 0 and 2 in the table must not produce a value between
        // their mean/gust. This asserts the lookup is an exact match, not
        // continuous interpolation across the index axis.
        FoliageWindDayGroupPoint[] table = [new(0, 0.0, 0.0), new(5, 1.0, 1.0)];

        (float meanAtUnlistedMidpoint, float gustAtUnlistedMidpoint) =
            RenderPackAtmospherePolicyEvaluation.FoliageWind(table, 2);

        Assert.Equal(0f, meanAtUnlistedMidpoint);
        Assert.Equal(0f, gustAtUnlistedMidpoint);
    }

    [Fact]
    public void EaseTowardTargetDoesNotMoveWithZeroDelta()
    {
        float result = RenderPackAtmospherePolicyEvaluation.EaseTowardTarget(
            current: 0.25f,
            target: 0.85f,
            deltaSeconds: 0f,
            transitionSeconds: 10f);

        Assert.Equal(0.25f, result);
    }

    [Fact]
    public void EaseTowardTargetConvergesWithoutOvershootOrDiscontinuity()
    {
        // Sample the same weather change (Clear 0.25 -> Rainy 0.85) many
        // times over the transition window at a fixed per-tick delta and
        // assert the sequence is monotonically non-decreasing and never
        // jumps by more than one tick's proportional share — "no
        // discontinuity across the delta window."
        const float start = 0.25f;
        const float target = 0.85f;
        const float transitionSeconds = 10f;
        const float tickSeconds = 0.1f;
        float current = start;
        float previous = current;
        // A fixed-rate-per-tick ease is exponential decay toward the
        // target, not a linear ramp: after N ticks the remaining gap is
        // (1 - tickSeconds/transitionSeconds)^N of the original gap. 4000
        // ticks (400 s of simulated time, 40x the transition window) leaves
        // a remaining fraction of (0.99)^4000 ~= 4e-18 — comfortably
        // converged without asserting a false linear-ramp expectation.
        const int ticks = 4000;

        for (int i = 0; i < ticks; i++)
        {
            current = RenderPackAtmospherePolicyEvaluation.EaseTowardTarget(
                current,
                target,
                tickSeconds,
                transitionSeconds);

            Assert.True(
                current >= previous - 1e-6f,
                $"tick {i}: value regressed from {previous} to {current}");
            Assert.True(
                current <= target + 1e-6f,
                $"tick {i}: value {current} overshot target {target}");
            previous = current;
        }

        Assert.True(MathF.Abs(current - target) < 0.01f, $"did not converge: {current}");
    }

    [Fact]
    public void EaseTowardTargetSnapsInOneStepWhenTransitionSecondsIsZeroOrLess()
    {
        float result = RenderPackAtmospherePolicyEvaluation.EaseTowardTarget(
            current: 0f,
            target: 1f,
            deltaSeconds: 0.001f,
            transitionSeconds: 0f);

        Assert.Equal(1f, result);
    }

    [Fact]
    public void EaseTowardTargetClampsAnOversizedDeltaInsteadOfOvershooting()
    {
        // A delta larger than the transition window (e.g. after a long
        // pause) must not overshoot past the target.
        float result = RenderPackAtmospherePolicyEvaluation.EaseTowardTarget(
            current: 0f,
            target: 1f,
            deltaSeconds: 1000f,
            transitionSeconds: 10f);

        Assert.Equal(1f, result);
    }
}